Respiratory systems provide breathable gas, such as oxygen, anesthetic gas, and/or air directly to a patient's mouth, nose, or airway to assist or facilitate breathing by the patient. A ventilator may be used as part of the respiratory system to drive the breathable gas to the patient through an inspiratory limb hose or conduit. An expiratory limb hose or conduit may be provided to allow air to expel from the patient.
It is typically desired to warm and impart humidity to the breathable gas before it is provided to the patient. For that purpose, many respiratory systems include a humidification system having a chamber for holding water and a heater unit including a heater adapted to heat the chamber. The chamber may be manually refillable, or there may be a water source to selectively fill the chamber as it empties. The breathable gas is passed through the chamber to be heated and humidified. An example of a heater unit and chamber arrangement is shown in U.S. Pat. Nos. 6,988,497 and 5,943,473. The inspiratory limb carries the heated and humidified gas to the patient and the expiratory limb, if present, carries exhaled air and possibly other gases from the patient. The inspiratory and/or expiratory limbs may also be heated such as by heater circuits comprised of one or more elongated wires running along the limb, such as through the interior thereof. An example of a breathing circuit with heated limbs is shown in U.S. Pat. No. 6,078,730.
Maintaining the desired temperature of gas(es) passing through this type of respiratory system may require adjusting the temperature of the heater in the heater unit and/or the heater circuits in the inspiratory and expiratory limbs in response to thermal feedback from the system. Thus, some respiratory systems include temperature probes at one or more locations, such as for sensing the temperature of the heated and humidified gas supplied to the patient. The temperature probes may be operatively coupled to the heater unit, which then adjusts the power levels to the heater and/or heater circuit(s) based at least in part on the measured temperatures. Current temperature probes for respiratory systems typically include a temperature-responsive device, such as a thermistor or other resistance temperature detector (RTD), within a protective housing. More specifically, the thermistor, which is typically held by epoxy within a cylindrical container, is typically inserted into an internal cavity of the housing and placed in thermal communication with an exterior wall at an end of the housing. Lead wires are electrically coupled to and extend away from the thermistor to be electrically coupled to an associated temperature cable at an opposite end of the housing for electrically communicating with the heater unit.
To hold or stabilize the thermistor within the internal cavity of the housing, an amount of potting compound is typically placed into the housing around the thermistor and lead wires, and then cured to encapsulate substantial portions of the thermistor and lead wires. But the nature of the typical potting compound and/or housing limits response time of the probe to transient or time-varying thermal conditions, and can present other drawbacks.